Archive for the "CMU" Category

Explanation of a Flash chip’s storage management routine

Saturday, August 8th, 2009

Hats off to Louis Gerbarg on his excellent write-up of how a Flash chip manages reads, writes, and most interestingly – deletes.  I have a relatively comprehensive understanding of how file systems work from classes back at CMU.  But back when I was taking those classes, Flash storage was basically non-existent in a file system context.  This post is definitely eye-opening and if you’re at all interested in how this stuff works, I highly recommend checking it out.  Here’s a quote that’ll get you interested in this stuff:

Okay, so lets assume for a second we have a 1MB flash device with 2 512KB blocks. This would be sold to the consumer as a 512KB flash drive, because some amount of the internal storage needs to be used for bookkeeping as we shall see.

And another quote:

Flash is a relatively complicated storage medium, and has its own view of the world. It works in terms of pages and blocks. Usually a page is the smallest amount of space you can reasonably read or write to a a flash chip (for our discussion, 4K), and a block is the smallest chunk of space you can erase at a time (for our discussion 128 blocks). With a fresh (unwritten block) all the bits are set to “1″, and during a write they can only be transition to “0.” That means in order to rewrite a page you must erase it first. This is a super important point, you can’t just go and erase a page of the flash, you need to erase the 128 contiguous pages contained in a whole block at a the same time.

And I thought tuning a filesystem to provide the best contiguous access to large files was interesting.  By comparison Flash garbage collection and bookkeeping algorithms must be fascinating.  In any case, I guess I’m just a little nostalgic reminiscing about CMU’s 15-412 Operating Systems course.

Carnegie Mellon effected by the recession

Monday, January 26th, 2009

lvl_carnegiemellon_logoAccording to a story by the Associated Press, Carnegie Mellon is feeling the recession. CMU’s endowment investments dropped in value about 30 percent, and preparing for the long-term effects of this drop, the University froze salaries and hiring, and put capital projects on hold.

This is definitely troubling.  I suppose we’re just starting to see the long-reaching effects of the recession, but I didn’t think it would be this devastating for educational institutions.  I’m not sure if other educational institutions are feeling this – I’m sure some without gigantic endowments will be feeling it quite a bit.  I wonder how institutions like MIT, Harvard, Columbia and NYU are faring?  There’s typically an increase in NIH funding for education and research under a Democratic presidency, but Barack Obama has some tough choices to make if he’s going to get the economy back in shape, and hopefully keeping the NIH budget won’t suffer because of that.

I suppose we’ll see.  Hopefully we won’t see any educational institutions going out of business without getting the bailout treatment the industrial and financial sectors are getting.